In general, inkjet printing machines or printers include at least one printhead that ejects drops or jets of liquid ink onto a recording or image forming media. A phase-change inkjet printer employs phase change inks that are solid at ambient temperature, but transition to a liquid phase at an elevated temperature. The melted ink can then be ejected by a printhead to form an ink image on an image receiving member. The ink image may be formed on a layer of release agent coating an intermediate imaging member, such as a rotating drum or belt, and then transferred to an image receiving substrate, such as a sheet of paper, as the substrate passes through a nip formed between a transfix roller and the intermediate imaging member. In other printing systems, the ink can be ejected directly onto printing media directed past the printheads.
Phase change ink printers often include one or more heaters that generate heat to maintain a supply of phase change ink in a liquid state in the printheads and inkjets for use during printing operations. Typically, the heaters are electrical heaters that consume electrical energy to generate the desired amount of heat. In order to reduce energy usage, phase change ink printers deactivate various components, including heaters, in the printer during a sleep mode to conserve energy. The ink held in the printheads and inkjets cools and solidifies when the heaters are deactivated.
While sleep modes enable a printer to operate with reduced electrical energy consumption, the solidification of phase change ink within the printer presents difficulties in printing high quality documents when the printer emerges from sleep mode. As phase change ink within an inkjet printing apparatus cools and solidifies, the ink contracts, allowing air into the pressure chambers and fluid conduits within the printheads. As the solidified ink heats and liquefies during a subsequent warm-up process, the air forms bubbles in the liquefied ink that can interfere with operation of the inkjets in the printhead. Additionally, during the warm-up process, both the ink and air bubbles expand due to the heat applied to the printheads. The expanding air bubbles may force some ink through the ejector nozzles, which is referred to as “drooling.” The drooled ink can contaminate other nozzles in the printheads or separate from the printheads and produce errant marks on the image receiving member.
To eliminate air bubbles in the liquefied ink within the printheads and to clear contaminants from the inkjet nozzles and external face of each printhead, the inkjet printing apparatus undergoes a “purge” operation, during which pressure applied to the reservoirs and passageways within the printheads urges the liquid ink and the air bubbles through the nozzles of the inkjets. In a purge operation, the inkjets emit a stream of ink that flows down the face of the printhead and is collected in a waste ink receptacle. The purge operation removes air bubbles from the inkjets in the printheads and other fluid conduits in the inkjet printing apparatus.
In some printing apparatus designs, a wiping operation occurs after the purge operation. In a wiping operation, a wiper blade engages the face of a printhead and moves across the printhead face. The wiper blade cleans residual ink and contaminants that remain on the face of the printhead after the purge operation. In existing printers, the purged ink and ink from a wiping operation is typically collected in a waste reservoir and is eventually discarded. In some instances, small amounts of purged ink dripping into the waste reservoir results in the ink solidifying immediately after landing in the waste reservoir. Over multiple purge operations, the ink solidifies to form tall narrow ink structures, known as stalagmites, rather than spreading out and filling the entire volume of the waste reservoir, reducing the ink capacity of the waste reservoir. In printers that enter sleep modes more often to reduce electrical energy consumption, the number of purge cycles and the corresponding amount of ink collected in the waste reservoir increases. Thus, improvements to phase change ink printers that reduce the amount of ink discarded from the printer and improve the collection of waste ink are desirable.